Zr-Co hydride stability against heating - cooling cycles in a closed system

The reversible absorption-desorption of hydrogen isotopes in metals can be affected during repeated heating cycles by the presence of impurity gases, such as O2, H2O, CO, CO2 or by the changes in characteristics of alloys in the presence of hydrogen in the system. Changes of hydrogen absorption-desorption characteristics of ZrCo alloy, during repeated heating-cooling, in a closed system has been studied. A measure of reversibility of hydriding reaction is the stability of equilibrium pressure at limiting temperatures of the cycles. After 43 heating cycles, between 100 and 6500 deg C (the pressure ranging between 2 and 0.3 bar), a reduction of storing capacity of 18% was observed. The cycling experiments carried out on Zr-Co alloy hydride reveals the presence of the absorption-desorption disproportion process. The effects of this process on the storing capacity are not as drastic as mentioned by other authors. The existing of a intermediate hydride reversible phase was made evident what suggest a mechanism a lot more complex of the absorption-desorption processes in the given experimental condition, the entire storing capacity of the alloy remaining unchanged. (authors)